Image capturing apparatuses include a virtual microscope apparatus in which, for example, an imaging region of a sample is in advance divided into a plurality of regions to image the divided regions at a high magnification and, thereafter, to synthesize the regions. In capturing images by using the virtual microscope as described above, conventionally, as conditions for picking up images of a sample such as a biological sample, a focus map which covers an entire region of the sample is set to capture images of the sample, while focus control is performed based on the focus map.
In preparation of the focus map, at first, an image capturing apparatus equipped with a macro optical system is used to capture an entire sample as a macro image. Next, the thus captured macro image is used to set an image pickup range of the sample and also the range is divided into a plurality of regions to set a focus obtaining position for each of the divided regions. After the focus obtaining position has been set, the sample is transferred to the image capturing apparatus equipped with a micro optical system to capture a focus position at the thus set focus obtaining position, thereby preparing a focus map with reference to the focus position.
However, in preparation of the above-described focus maps, there has been a problem that processing needs time. Further, suppression of intervals and the number of focuses to be obtained would reduce the time necessary for the processing. In this case, however, there has been a problem of reduction in focus accuracy. Therefore, development of dynamic focus for capturing images of a sample at a high magnification, with a focus position being obtained, is now underway. The dynamic focus is a method in which a present direction of the focus position deviating from the height of an objective lens is detected based on a difference in light intensity or a difference in contrast between an optical image which is focused at the front of an optical image made incident into an imaging device for capturing an image (front focus) and an optical image which is focused at the rear thereof (rear focus), thereby allowing the objective lens to move in a direction at which the deviation is cancelled to capture an image.
A microscope system disclosed, for example, in Patent Document 1, is provided with a second imaging unit which images a region at the front of a region imaged by a first imaging unit, an automatic focusing control unit which adjusts a focusing position of an objective lens at an imaging position of the first imaging unit based on an image picked up by the second imaging unit, and a timing control unit which synchronizes timing at which a divided region moves from an imaging position of the second imaging unit to the imaging position of the first imaging unit with timing at which an image forming position of the divided region imaged by the second imaging unit is positioned at an imaging area of the first imaging unit depending on a distance between the divided regions and a speed at which a sample moves. Further, in a microscope apparatus disclosed, for example, in Patent Document 2 or Patent Document 3, a glass member is used to make a difference in optical path length inside a light guiding optical system for focus control.